Safety device for cutting off gas pipelines

ABSTRACT

A thermal safety device for cutting off gas pipelines, wherein gas transfer is prevented by the safety device when temperature increases in the section of the gas pipeline placed downstream from the safety device, especially when connected gas apparatuses are in a closed position maintains production costs and dimensions at a level as low as possible. The safety device includes a check valve which prevents backflow from the gas pipeline which is placed downstream from the device. The inventive device also includes a pressure sensitive element placed downstream from the safety device which is actuated by the pressure in the pipeline. The pressure sensitive element is coupled to a cut-off valve in such a way that when pressure increases in the downstream pipeline the valve prevents gas from flowing into the pipeline.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a safety device for cutting off gas pipelineswhen temperature increases in an unacceptable way according to thepreamble of the first patent claim.

Such thermal valve safety devices that are employed in pipelines, suchas upstream from gas apparatuses, gas meters, etc., are available in alarge variety of designs. They are used to interrupt gas supply beforetemperature increases at the aforementioned gas apparatuses to suchlevel that their external tightness is jeopardised.

EP 118 152 A1 describes a valve in which a ball is kept respectively inopen and, after reaching a limit temperature in closed position both bya spring and also by an alloy with thermal shape memory, with the springbeing in such shape that automatic opening is impossible after closing.

The disadvantage of this solution is that the component of an alloy withthermal shape memory, located in the housing interior, has to besubjected to the higher temperature in order to achieve the desiredclosing of the valve. This means that the entire valve has to be heatedin order to attain a response of the thermo-sensitive part by conductionof said heat. And it is necessary to place such valve immediatelyadjacent to each component that is jeopardised by temperature increasein order to detect the temperature in the area and, if need be, cut offthe gas pipeline.

EP 343 615 A1 describes a valve with a cone as cut-off element. In thissolution a guide rod is led through a valve cover and connects said plugwith a fuse body that is pre-tensioned against the cover by means of apressure spring. Softening of the fuse body removes the guide rod fromthe former so that, under the impact of the pressure spring, the plugcan move abruptly in the closing direction.

Also this solution has the disadvantage that, on the one hand, thethermo-sensitive element is positioned in the housing interior and,hence, also the entire valve has to be heated and, on the other, such avalve has to be placed directly adjacent to each component that isjeopardised by temperature increase.

A thermal safety valve is also known from the utility model DE 94 20607. This thermal safety valve is essentially of the same constructionas the solution described above, i.e. the housing is provided with asoft solder which keeps a cut-off element, in this case a valve cone, inopen position. Additionally a heating jacket, which is preferablyelectrically heatable, is provided at the valve housing in the area ofthe internal soft solder, so that the safety valve does not only actuateautomatically after the soft solder is directly subjected to the highertemperature but which also facilitates its remote actuation.

The disadvantage of this solution is, that besides its complicatedconstruction, it is necessary to provide additionally a source ofauxiliary energy, piping and respective actuation elements.

EP 637 457 A1 describes an automatic closing device for a shut-offdevice. The element inhibiting the closing force has at least onepressure-actuated hollow body with a variable volume with a ratedbreaking point of a material whose melting temperature is adjusted to adefined limit value temperature. Upon achieving or exceeding said limitvalue temperature the closing operation is triggered by melting of thebreaking point material and a subsequent pressure relief. The force ofpressure in the hollow body is reduced and the closing force isactivated. The rated breaking point can be executed as a reaction linethat can be laid at any distance from the shut-off device so that a fireoccurring in the reaction line yet at a distance from the shut-offdevice triggers the closing action.

The disadvantage of the latter solution is that the reaction line has tocover the entire area of the unit to be protected which, particularly incase of large units, entails disproportionately high costs.

DE 296 12 921 U1 describes a cut-off device for a gas pipeline systemwith a cut-off element that is kept in open position by at least oneclosing force-inhibiting element. The element has at least onepressure-actuated hollow body with a variable volume that is connectedto a so-called function line consisting of a material whose meltingtemperature is adjusted to a defined limit value temperature. Melting ofthe function line causes a pressure drop in the hollow body and theclosing force actuates the cut-off element so that the cut-off device isclosed and the flow through the pipeline is discontinued. The pipelineoutlet is additionally provided with a backflow check valve which, upona pressure drop in the pipeline, prevents a gas backflow from thedownstream pipeline.

In this cut-off device there is a pressure in the hollow body and thefunction line which is required to keep the cut-off element in the openposition. Said pressure, however, is independent of the pressure in thegas pipeline.

It is also known that so-called gas flow control valves are used toautomatically cut off gas pipelines. Said gas flow control valves areused to interrupt gas supply upon increase of gas consumption beyond adefined value.

The disadvantage of such gas flow control valves is that, in case of adamage at the gas pipeline, e.g. by a fire, and with a closed gasapparatus the gas volume flowing from the leak will have to be largerthan the gas volume flow otherwise required for the operation of the gasapparatus before the gas flow control valve is closed.

The invention is focusing on the issue of developing a safety device forcutting off gas pipelines of the described type wherein the gas transferthrough the safety device is prevented when temperature increases in thesection of said safety device placed downstream from the gas pipeline,especially when connected gas apparatuses are in a closed position. Inaddition, it shall be possible to avoid an excessive pressure rise inthe downstream pipeline. The aim of the invention is to maintainproduction costs and dimensions at a level as low as possible. Accordingto the present invention the problem is solved by providing a safetydevice with a check valve that prevents a backflow from the gas pipelinewhich is placed downstream from said device and by arranging a pressuresensitive element which is actuated by the pressure in the pipelinedownstream from said safety device. Said pressure sensitive element iscoupled to a cut-off valve in such a way that when pressure increases inthe downstream pipeline said valve prevents gas from flowing into thepipeline.

Thus a solution has been found that removes the disadvantages of theprior art that a thermal element in the housing interior has to beactuated by the higher temperature in order to achieve the desiredclosing of the valve. It is also no longer necessary to place such valvedirectly adjacent to each component that is jeopardised by a temperatureincrease in order to detect the temperature in this area and, if needbe, cut off the gas pipeline. Further distinguishing features of thissolution are above all its simplicity and production dimensions.

Further advantageous arrangements of the invention are described in theother patent claims. In order to prevent, for instance, the pressurerise from becoming excessively high after a temperature increase in thedownstream pipeline a backflow can be released from the downstreampipeline by the check valve or a by-pass circumventing said check valve,after the gas transfer into the downstream pipeline has been cut off bythe cut-off valve, with the cut-off valve also releasing backflow fromthe downstream pipeline.

In order to largely simplify assembly the movable cut-off element of thecheck valve can be a piston or a diaphragm which is loaded by a springand/or its own weight against the gas flow direction. The piston ordiaphragm disk can simultaneously form the pressure sensitive element.

A particularly advantageous form of execution in terms of manufacturingand cost-effectiveness is achieved when a rising pressure in the gaspipeline placed downstream from the safety device moves the piston intoa bore and a return movement of the piston is prevented by theengagement of a latching stop. The bore is sealed by a flexible sealingat the piston.

In order to obtain a stroke motion of the piston by an initially lowfriction between piston and seat already at a low pressure andsimultaneously ensure tightness at rising pressure the bore ispreferably tapered in the moving direction of the piston.

Preferably, the section of the bore that is assigned to the piston afterthe engagement of the latching stop has an expansion. The fact that thediameter of said expansion is larger than the diameter of the pistonwith flexible sealing creates a gap between piston and expansion throughwhich the pressure in the downstream pipeline is relieved. Followingsaid pressure relief the piston, under the impact of a spring and/or itsown weight as well as the latching stop, is again outside of theexpansion and its flexible sealing seals the bore.

A particularly simple construction in terms of manufacturing is obtainedwhen the latching stop comprises an expansion of the bore and a flexiblesealing. In this case the diameter of the expansion is smaller than thatof the piston with a flexible sealing. In addition, theexpansion-to-bore transition has a limit stop.

A further form of execution of the inventive safety device for cuttingoff gas pipelines is attained by coupling the pressure sensitive elementto an already known gas flow control valve in such a way that the gasflow control valve is in a closed position after a pressure rise in thedownstream pipeline. This can be achieved, e.g., by the pressuresensitive element releasing the lock of a pre-tensioned spring whenpressure increases and the gas flow control valve is moved into itsclosed position by the impact of the spring.

Said coupling with a gas flow control valve makes it possible to safelyclose the downstream pipeline in an emergency case, irrespective of theoperating state of the connected gas apparatus.

The axial movement of the piston is preferably limited on either side bya seat with the seat upstream from the piston forming the check valvetogether with the piston, while the seat downstream from the pistonforming the gas flow control valve together with the piston.

In order to avoid an abrupt movement of the piston from its operatingposition upon switching on the gas apparatus, and thus a prematureresponse of the gas flow control valve, the piston has, at least at onefront face, an extension which slides with loose fit in a guide aperturewhich is gas-tight closed at the front side. Thus, the opening processis damped.

Further advantageous executions are obtained when the safety device hasa manipulator that can be externally actuated and is used to take thespring into the pre-tensioned and locked position or/and with which thesafety device in a closed position can be brought into its initialposition.

Its is also possible to arrange a number of safety devices in a gasdistributor.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a more detailed description of the invention by means ofseveral practical examples. The figures show the following:

FIG. 1 is a sectional view of an inventive safety device with ball valvein accordance with the present invention,

FIG. 2 is a fragmentary sectional view of another embodiment of aninventive safety device shown in an operating position,

FIG. 3 is a view similar to that of FIG. 2 but showing the inventivesafety device shown in a pressure compensation position,

FIG. 4 is another view similar to FIG. 2 but showing inventive safetydevice shown in a safety position,

FIG. 5 is another embodiment of an inventive safety device shown with agas flow control valve, shown in an operating position,

FIG. 6 is a view of the embodiment shown in FIG. 5 but shown in a safetyposition,

FIG. 7 is a sectional view of a further embodiment of an inventivesafety device shown with a gas flow control valve, and in a operatingposition,

FIG. 8 is a view of the embodiment of FIG. 7 shown with a gas flowcontrol valve, and in a pressure compensation position,

FIG. 9 a view of the embodiment of FIGS. 7 and 8 shown in a safetyposition,

FIG. 10 is a view of the embodiment shown in FIGS. 7, 8, and 9 but shownin a working position,

Fig. 11 is a view of the embodiment of FIGS. 7, 8 and 9 shown with aclosed gas flow control valve,

FIG. 12 is a view of the embodiment of FIGS. 7, 8 and 9 but shownincorporating a manipulator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventive safety device that is explained thereunder in greaterdetail is described in FIG. 1 on the basis of a ball valve that is knownto the expert and used here as a cut-off valve 1. The safety devicecomprises a tubular housing 11 with a connection at either end, in thiscase drawn as a thread. It goes without saying that also anotherconnection types are possible. Next to the inlet-side internal thread acheck valve 2 is centrically arranged in the housing 11. The flowdirection prevailing in the pipeline under normal operation conditions,hereinafter referred to as flow direction, is marked by an arrow.

The check valve 2 in this case comprises two punched disks 21/22arranged behind each other in flow direction, which have at their centrea slide bearing 211/221 each for an axially movable tappet 23, to whicha piston 24 is fastened between the punched disks 21/22. A pressurespring 25 actuates on the front face of the piston 24 opposite the gasinlet 113 whose other end is braced against the punched disk 22. Inorder to ensure gas tightness of the check valve 2 in closed position anO-ring is arranged as a flexible sealing 242 in a circumferential groove241 of the piston 24, with the bore 26, tapered in flow direction andmade through the internal wall of housing 11, providing the valve seatfor the check valve 2.

The housing 11 also comprises a ball that is used as a shut-offmechanism 12, is pivot-borne in sealings serving as seat 16 and has athrough-hole 121 in longitudinal direction of the housing 11. A pivotingaxis 14, borne in a gastight manner on O-rings 13 and solidly connectedto the tubular yoke 112 of the ball valve 1 housing 11, which leadsradially to the outside is, on the one hand, keyed to the ball 12 and,on the other, to a manipulator 15 with which the ball valve 1 can bebrought into its open or closed position by means of a swivellingmovement. Construction and mode of action of ball valve 1 are known tothe expert, hence, there is no need for a detailed explanation here.

A pressure sensitive element 3 is arranged between the ball valve 1 andthe check valve 2. The pressure sensitive element 3 comprises apot-shaped metal bellows 31 that is fixed in a gastight manner to thefront face of the housing 11 internal wall and projects radially intothe housing 11 interior and on whose bottom a tappet 32 is fixed whoseother end is led lengthwise movable inside a through-hole 111 in thehousing 11 wall. The tappet 32 supports a thrust piece 33 that projectsfrom the housing 11 to the outside.

The yoke 112 bears an L-shaped lever in a pivotable manner whose onelimb 341 has an aperture 342 into which the end of the thrust piece 33projects that is led out of the housing 11. The other limb 343 sitsclose to the manipulator 15 when the ball valve 3 is in open position. Atorsion spring 35 is axially led on the yoke 112 whose one end is bracedagainst the housing 11 while the other end sits close to the limb 343 sothat the latter loads the manipulator 15 in the closing direction of theball valve 1 and the thrust piece 33 forms a latch for the lever.

The function of the inventive safety device that is described in thisfirst practical example is as follows:

In the operating position the ball 12 of the ball valve 1 is open. Ifthe gas apparatus located at the end of the downstream gas pipeline thatis not depicted is out of operation, the check valve 2 is in its closedposition. If now there is a temperature increase, e.g. by fire, in thesection downstream from gas pipeline the heat causes a pressure rise insaid pipeline. This pressure rise effects a stroke of the metal bellows31 which, by means of the tappet 32, lifts the thrust piece 33 out ofthe through-hole 111 and hence its catch. Under the force of thetensioned torsion spring 35 the limbs 341 is not arrested any longer andhence the limb 343 and thus also the manipulator 15 are rotated into theclosing direction and the ball valve 1 is closed. The safety device isin the safety position.

In order to prevent an excessive pressure rise in the downstreampipeline the safety device described in this practical example can havean additional bypass. A pressure control valve that is known to theexpert and hence not further explained is functionally arranged in saidbypass, which connects the up- and downstream pipeline while bypassingthe safety device, in such a manner that it is always shut in the gasflow direction while a pressure compensation from the downstream to theupstream pipeline is possible. Said pressure control valve has to beadjusted in such a way that it responds only after a closing of thecut-off valve 1.

FIGS. 2 to 4 are schematic representations of a second modifiedpractical example of an inventive safety device which is particularlydistinguished by its simple construction. This inventive safety devicecomprises a housing 11 with a gas inlet 113 and a gas outlet 114depicted as a corner arrangement in this practical example. Gas inlet113 and gas outlet 114 are each provided with a connection for a gaspipeline not depicted here.

The housing 11 comprises a check valve 2 consisting of a piston 24 and abore 26 in the housing 11 which forms a valve seat that is preferablytapered in flow direction. In flow direction downstream from the bore 26is a piston 24 which, as in the first practical example, has an O-ringin a circumferential groove 241 as a flexible sealing 242 in order toensure the gas tightness of the check valve 2 in closed position. Thepiston 24 is loaded by its own weight against the flow direction.

In addition, the piston 24 has at one side a front face extension 243that is led into an aperture 115 in the housing 11. The aperture 115 isfitted with a groove 116 in which a radial spring-loaded element 117,e.g. a wire strap, is partially borne while its remainder sits in theaperture cross-section.

The extension 243 has a first contraction 244 in whose area aspring-loaded element 117 is positioned in the operating position (FIG.2). The limitation of the contraction 244 opposite the piston 24 forms afirst limit stop 245 that limits the opening stroke of the piston 24. Bycontrast the limitation of the first contraction 244 facing the piston24 has a tapered transition 246 so that upon reaching the spring-loadedelement 117 the latter expands into its groove 116 until a secondcontraction 247 arranged on the shaft 243 between piston 24 and firstcontraction 244 catches. By contrast the limitation of the secondcontraction 247 facing the first contraction 244 forms a second limitstop 248 that limits the stroke of the piston 24 in such a way that itcannot leave the bore 26 in flow direction. Thus, the second contraction242 and the second limit stop 248 form a latching stop 27.

A pressure spring 25 is led on the extension 243 between housing 11 andpiston 24. In operating position this pressure spring 25 is freelymovable in longitudinal direction and thus ineffective (FIG. 2).

The mode of operation of the inventive safety device described in thissecond practical example is as follows:

In this practical example the piston 24, in combination with the bore26, does not only take on the function of the check valve 2 but alsothat of the cut-off valve 1 as well as that of the pressure sensitiveelement 3 which results in the simple construction already mentionedelsewhere.

If the gas apparatus, placed at the end of the downstream gas pipelinethat is not depicted, is out of operation the check valve 2 is closed(FIG. 2). The spring-loaded element 117 is in the first contraction 244,whose limit stop 245 limits the opening stroke when the gas apparatus isin switched on state. If there is now a temperature increase, e.g. dueto fire, in the section of the downstream gas pipeline the generatedheat causes a pressure rise in this pipeline. This pressure rise effectsa stroke of the piston 24 against the flow direction and against theforce of the then acting pressure spring 25 that is braced against thehousing 11 and the piston 24. At the same time the stroke moves theextension 243 towards the spring-loaded element 117 so far that thespring-loaded element 117 slides across the conical transition 246 intothe second contraction 247. At a respectively high and undesiredpressure rise the stroke of the piston 24 creates a gap between theflexible sealing 242, formed by the O-ring, and the bore 26 whichresults in a pressure relief of the downstream pipeline (FIG. 3).Following said pressure relief the force of the pressure spring 25returns the piston 24 into the bore 26, serving again as seat 16 of thecut-off valve 1. The latching stop 27 prevents the check valve 2 fromopening. The safety device is in the safety position.

FIGS. 5 and 6 are schematic representations of a third practicalexample, as a modification of the second one, of an inventive safetydevice wherein there is no pressure relief.

This inventive safety device also comprises a housing 11 with a gasinlet 113 and a gas outlet 114 depicted as a corner arrangement in thispractical example. Gas inlet 113 and gas outlet 114 are each providedwith a connection for a gas pipeline not depicted here.

Also in this practical example the housing 11 is provided with a checkvalve 2, consisting of a piston 24 and a valve seat formed by a bore 26in the housing 11, which is preferably tapered in flow direction.Downstream from the bore 26 in flow direction there is a piston 24which, as in the first and second practical examples, has an O-ring in acircumferential groove 241 as flexible sealing 242 to ensure the gastightness of the check valve 2 in closed position. The piston 24 isloaded by its own weight against the flow direction. Upstream the bore26 verges into an expansion 262 whose diameter is smaller than that ofthe piston 24 with the flexible sealing element 242. The transition fromthe expansion 262 to the bore 26 has a limit stop 248 so that theflexible sealing element 242 and the expansion 262 form a latching stop27 suited for low line pressures. For higher line pressures the latchingstop 27 can be executed in such a way that the piston 24 one side has afront-face extension 243 that is led in the guidance section 18 of anaperture 115 as long as the piston is outside of the expansion 262. Themode of operation of the inventive safety device described in this thirdpractical example, wherein, for the sake of simplicity, there is nopressure relief, as already mentioned elsewhere, is as follows:

If the gas apparatus, placed at the end of the downstream from gaspipeline that is not depicted, is out of operation the check valve 2 isclosed (FIG. 5). The extension 243 is in the guidance section 18. If nowthere is a temperature increase, e.g. due to fire, in the section of thedownstream gas pipeline the generated heat causes a pressure rise inthis pipeline. This pressure rise effects a stroke of the piston 24against the flow direction and the piston 24 gets into the expansion262. The latching stop 27 prevents an opening of the check valve 2. Thesafety device is in the safety position.

In the version that is suited for higher line pressures the stroke movesthe extension 243 in the aperture 115 so far that it leaves the guidancesection 18 and, due to a toeing of the extension (Fig. 6), gets into thesafety position.

FIGS. 7 to 12 are schematic representations of a modified practicalexample of an inventive safety device. In this practical example thesafety device is combined with a gas flow control valve 4.

This inventive safety device comprises a housing 11 with a gas inlet 113and a gas outlet 114 depicted as a corner arrangement in this practicalexample. Gas inlet 113 and gas outlet 114 are each provided with aconnection for a gas pipeline not depicted here.

The housing 11 comprises a check valve 2 consisting of a piston 24 and abore 26 in the housing 11 which form a valve seat that is preferablytapered in flow direction. In flow direction downstream from the bore 26is a piston 24 which, as in the first practical example, has an O-ringin a circumferential groove 241 as a flexible sealing 242 in order toensure the gas tightness of the check valve 2 in closed position. Thepiston 24 is loaded by its own weight against the flow direction.

In flow direction downstream from the piston 24 the housing 11 has asecond contraction which is formed as the seat 41 of an already knowngas flow control valve 4 whose shut-off mechanism is formed by a piston24 in this practical example. The piston 24 is solidly connected to alongitudinally movable tappet 23 that is led in a slide bearing 221,arranged in a punched disk 22 that is placed in flow directiondownstream from the seat 41 in the housing 11, and in an aperture 115.Preferably the tappet 23 has a guide collar 231 that forms a loose fitwith the aperture 115. Next to the aperture 115 is a bore 118 leadingoutside that is closed in a gastight manner by an inspection plug 17.The bore 118 is arranged in a staggered way to the aperture 115 so thatat least a unilateral locating edge 119 is formed for a thrust piece 33that is placed in the bore 118 but otherwise longitudinally movable andbraced against the inspection plug 17 by a pressure spring 25, andloaded towards the tappet 23. The front face of the thrust piece 33facing the tappet 23 has a funnel-shaped receiver 331 for the tappet.

The mode of operation of the inventive safety device with a gas flowcontrol valve 4 described in this fourth practical example is asfollows:

Also in this practical example the piston 24, in combination with a seatformed by the bore 26, does not only take on the function of the checkvalve 2 but also that of the cut-off valve 1 as well as that of thepressure sensitive element 3 which results in the simple constructionalready mentioned elsewhere. At the same time the piston 24 is used as ashut-off mechanism for the gas flow control valve 4 whose seat 41 isintegrated into the housing 11.

If the gas apparatus, placed at the end of the downstream from gaspipeline that is not depicted, is out of operation the check valve 2 isclosed (FIG. 7), i.e. the piston 24 is in the area of the bore 26. Inorder to prevent upon switching on of the gas apparatus that an abruptopening stroke moves the piston 24 against the seat 41 the tappet 23 hasa guide collar 231, already mentioned above, which, in combination withthe loose fit to the aperture 115 acts as an attenuator.

If there is now a temperature increase, e.g. due to fire, in the sectionof the downstream gas pipeline the generated heat causes a pressure risein this pipeline. This pressure rise effects a stroke of the piston 24against the flow direction which initially moves the tappet 23 into thefunnel-shaped receiver 331 and then lifts the thrust piece 33, againstthe force of the acting pressure spring 25 that is braced against thethrust piece 33 and the inspection plug 17, from the locating edge 119and thus releases the locking.

At a respectively high and undesired pressure rise the stroke of thepiston 24 creates a gap between the flexible sealing 242, formed by theO-ring, and the bore 26 which results in a pressure relief of thedownstream pipeline (FIG. 8). Following said pressure relief the forceof the pressure spring 25 moves the piston 24 towards the seat 41 whichthan serves as the seat 16 of the cut-off valve 1 (FIG. 9). The safetydevice is in the safety position.

After the removal of the inspection plug 17 the thrust piece 33 can bereturned to its initial position and the pressure spring 25 tensioned.

If the gas apparatus located at the end of the downstream gas pipelinethat is not depicted is in operation, the check valve 2 is in its openposition. It is in a working position (FIG. 10). The piston 24 is in thearea between the bore 26 and the valve seat 41. If now there is anincrease in the gas volume flow in the downstream gas pipeline thepiston 24 is moved towards the seat 41, i.e. the gas flow control valve4 closes and the safety device is in the safety position (FIG. 11).

FIG. 12 shows the practical example of an inventive safety device thatis schematically represented in FIGS. 7 to 11 and described in detailalready elsewhere with an additional manipulator 15 that can beexternally actuated and is borne in a gastight manner in a duct in thehousing 11 not depicted here. The piston 24 can be lifted from the seat41 by actuating said manipulator 15. Thus, the safety device in closedposition can be returned to its initial position in non-defective gaspipelines and with closed gas apparatus.

As a matter of course the inventive safety device is not restricted tothe shown practical examples. There are rather alterations andmodifications possible without leaving the scope of the invention.Connections can be varied, for example. Also the described combinedsub-assemblies can be executed as individual components or the describedparts can be replaced by equivalents. Also a combination of thepractical examples described, e.g., in FIGS. 2 to 6 is possible.Moreover, the inventive safety device can also have a manipulator 15that is externally operable as additionally schematically representedonly in FIG. 12 for the fourth example. Also the arrangement of severalinventive safety devices in a gas distributor is possible.

What is claimed is:
 1. A safety device for cutting off a gas pipelineabove a predetermined temperature, the safety device comprising: a checkvalve to prevent a backflow from a portion of a gas pipeline situateddownstream to the safety device; and a pressure-sensitive elementcoupled to a cut-off valve in such a way that in case of rising pressurein the pipeline, the cut-off valves stops the gas flow through thepipeline, the pressure-sensitive element pressurized by a pressureprevailing in the downstream portion of the pipeline being locatedwithin the gas pipeline, the check valve for preventing the backflowformed by the cut-off valve being situated within the gas pipelineupstream to the pressure-sensitive element.
 2. A safety device forcutting off gas pipelines according to claim 1, wherein the check valvereleases a backflow from the downstream portion of the pipeline after agas transfer into the downstream portion of the pipeline has been cutoff to prevent inadmissible overpressure in the downstream portion ofthe pipeline.
 3. A safety device for cutting off gas pipelines accordingto claim 1, wherein the movable closing element of the check valve is apiston or a diaphragm disk that is loaded by a spring and/or its ownweight against the gas flow direction and that the piston or thediaphragm disk forms the pressure sensitive element.
 4. A safety devicefor cutting off gas pipelines according to claim 3, wherein the pistonis movable in response to a rising pressure in the downstream portion ofthe pipeline into a bore and wherein an engaging latching stop preventsa return movement of the piston and that said piston with a flexiblesealing seals the bore.
 5. A safety device for cutting off gas pipelinesaccording to claim 4, wherein the bore is tapered in the movingdirection of the piston.
 6. A safety device for cutting off gaspipelines according to claim 4, wherein a section of the bore that isassigned to the piston after the engagement of the latching stop has anexpansion whose diameter is larger than that of the piston with aflexible sealing and that the bore is sealed by the piston with theattached flexible sealing after a pressure relief in the downstreampipeline through the created gap and under the impact of a spring and/orits own weight as well as the latching stop.
 7. A safety device forcutting off gas pipelines according to claim 4, wherein the latchingstop consists of an expansion of the bore and the flexible sealing, thetransition from the expansion to the bore having a limit stop.
 8. Asafety device for cutting off gas pipelines according to claim 1,wherein the pressure sensitive element is coupled to a gas flow controlvalve in such a way that the gas flow control valve is in a closedposition when the pressure increases in the downstream portion of thepipeline.
 9. A safety device for cutting off gas pipelines according toclaim 8, wherein a pressure sensitive element releases the lock of apre-tensioned spring when pressure increases and that the gas flowcontrol valve moves into its closed position under the impact of aspring.
 10. A safety device for cutting off gas pipelines according toclaim 8, wherein the axial movement of the piston is limited on eitherside by a seat, the seat upstream from the piston forming the checkvalve together with the piston the seat downstream from the pistonforming a gas flow control valve together with the piston.
 11. A safetydevice for cutting off gas pipelines according to claim 10, wherein thepiston has an extension on at least one front face which slides with aloose fit in a guidance aperture whose front face is closed in agastight manner.
 12. A safety device for cutting off gas pipelinesaccording to claim 9, wherein the safety device has an externallyoperable manipulator with which the spring can be brought into apre-tensioned and latched position.
 13. A safety device for cutting offgas pipelines according to claim 1, wherein the safety device has anexternally operable manipulator with which the safety device in closedposition can be returned into its initial position.
 14. A safety devicefor cutting off gas pipelines according to claim 2, wherein the checkvalve includes a movable closing element in the form of a piston or adiaphragm disk that is loaded by a spring and/or its own weight againstthe gas flow direction and that the piston or the diaphragm disksimultaneously form a pressure sensitive element.
 15. A safety devicefor cutting off gas pipelines according to claim 14, wherein the pistoncan be moved by rising pressure in the downstream pipeline into a borewherein an engaging latching stop prevents a return movement of thepiston and that said piston with a flexible sealing seals the bore. 16.A safety device for cutting off gas pipelines according to claim 5,wherein the section of the bore that is assigned to the piston after theengagement of the latching stop has an expansion whose diameter islarger than that of the piston with a flexible sealing and that the boreis sealed by the piston with the attached flexible sealing after apressure relief in the downstream pipeline through the created gap andunder the impact of a spring and/or its own weight as well as thelatching stop.
 17. A safety device for cutting off gas pipelinesaccording to claim 5, wherein the latching stop consists of an expansionof the bore and the flexible sealing, the transition from the expansionto the bore having a limit stop.
 18. A safety device for cutting off gaspipelines according to claim 15, wherein in that the section of the borethat is assigned to the piston after the engagement of the latching stophas an expansion whose diameter is larger than that of the piston with aflexible sealing and that the bore is sealed by the piston with theattached flexible sealing after a pressure relief in the downstreamportion of the pipeline through the created gap and under the impact ofa spring and/or its own weight as well as the latching stop.
 19. Asafety device for cutting off gas pipelines according to claim 15,wherein the latching stop consists of an expansion of the bore and aflexible sealing wherein the diameter of said expansion is smaller thanthat of the piston with a flexible sealing and that the transition fromthe expansion to the bore has a limit stop.
 20. A safety device forcutting off gas pipeline according to claim 1, further comprising abypass circumventing the check valve for preventing an inadmissibleoverpressure in the downstream portion of the pipeline, the bypass forreleasing a backflow from the downstream portion of the pipeline after agas transfer into the downstream portion of the pipeline has been cutoff.